1. Field of the Invention
The present invention relates to a sound volume correcting device, a sound volume correcting method, and a sound volume correcting program, which can be suitably used in a sound output unit of an electronic apparatus such as a television broadcast receiver.
2. Description of the Related Art
When a broadcast channel received by a television broadcast receiver is switched or when plural input devices are switched in an AV center of an audio-visual (AV) system, an output sound volume may be greatly changed due to a level difference between contents.
In this case, it is necessary for a user to adjust the sound volume using a remote controller or the like so as to obtain his preferred sound volume and thus may find it troublesome.
Even with the same content (for example, on the same broadcast channel or during the same broadcast program), the output sound volume varies depending on a variation between commercial message (CM) breaks or scenes, thereby giving an unpleasant feeling.
Various sound volume correcting techniques have been suggested to solve the above-mentioned problem. A sound volume control method using an AGC (Auto Gain Control) is widely known as an example thereof.
FIG. 26 is a block diagram illustrating the configuration of a sound volume corrector using the AGC. In the example shown in FIG. 26, left and right channel input audio signals SiL and SiR are corrected in sound volume.
In this example, the left and right channel input audio signals SiL and SiR are supplied to variation gain amplifiers 1L and 1R of which the gains are variably controlled on the basis of a gain control signal.
The left and right channel input audio signals SiL and SiR are added to each other by an adder 2. The added output signal from the adder 2 is made to be half the gain by an amplifier 3 and is then supplied to an average level detector 4, and the average level of the added output signal is detected by the average level detector 4.
The average level detected by the average level detector 4 is supplied to a gain control signal generator 5. The gain control signal generator 5 compares the average level from the average level detector 4 with a predetermined reference level, generates a gain control signal so that the difference between both levels is zero using the comparison result, and supplies the generated gain control signal to the variable gain amplifiers 1L and 1R.
In the variable gain amplifiers 1L and 1R, the gain is variably controlled on the basis of the gain control signal from the gain control signal generator 5. In this case, the gains of the left and right channel input audio signals SiL and SiR are controlled by the variable gain amplifiers 1L and 1R so that the average level of the added output signal from the adder 2 is equal to the reference level.
As a result, left and right channel output audio signals SoL and SoR obtained from the variable gain amplifiers 1L and 1R are automatically corrected to a constant level of sound volume by adjusting a small sound to be great and a great sound to be small.
Various sound volume correcting methods have been suggested in addition to the sound volume correcting method using the AGC. For example, Japanese Patent No. 3321820 discloses a method of controlling a sound volume within a constant range by controlling a compressor to adjust an output sound level to be smaller than an input sound level when a great level of sound is input.